fix not up-to-date unit tests.
Faster Sum32(data []byte) shortcut.

benchmark           old ns/op    new ns/op    delta
Benchmark32_1              26            8  -68.50%
Benchmark32_2              28            9  -66.73%
Benchmark32_4              26            7  -70.08%
Benchmark32_8              29            9  -67.69%
Benchmark32_16             32           12  -62.54%
Benchmark32_32             39           18  -53.33%
Benchmark32_64             54           31  -42.33%
Benchmark32_128            84           58  -30.37%
Benchmark32_256           150          116  -22.67%
Benchmark32_512           273          227  -16.85%
Benchmark32_1024          523          449  -14.15%
Benchmark32_2048         1012          894  -11.66%
Benchmark32_4096         2014         1792  -11.02%
Benchmark32_8192         4189         3559  -15.04%

benchmark            old MB/s     new MB/s  speedup
Benchmark32_1           37.54       119.39    3.18x
Benchmark32_2           70.39       211.69    3.01x
Benchmark32_4          151.30       506.24    3.35x
Benchmark32_8          275.73       853.40    3.10x
Benchmark32_16         494.69      1324.19    2.68x
Benchmark32_32         820.16      1760.81    2.15x
Benchmark32_64        1183.45      2051.59    1.73x
Benchmark32_128       1518.72      2180.34    1.44x
Benchmark32_256       1704.27      2194.85    1.29x
Benchmark32_512       1873.52      2247.43    1.20x
Benchmark32_1024      1955.82      2276.88    1.16x
Benchmark32_2048      2022.21      2289.87    1.13x
Benchmark32_4096      2033.24      2284.64    1.12x
Benchmark32_8192      1955.41      2301.33    1.18x